Deficiency of surfactant can result in Respiratory Distress Syndrome (RDS) in the prematurely born infant. The etiology of RDS is multifactorial and/or multigenetic. A genetic contribution to the etiology of RDS has been suggested by a number of studies. Because of the importance of the surfactant proteins in surfactant structure, metabolism and function in our present study, we propose to study whether genetic alterations in regions within or flanking the surfactant protein genes associate with RDS. The key objectives are: 1) characterize genetic markers within and in flanking sequences of the surfactant protein (SP) genes with emphasis on SP-B; 2) study associations of the SP markers to determine haplotypes; and 3) study associations between the markers and/or haplotypes of various groups of individuals with and without RDS. The study population will include unrelated individuals born prematurely or at term with or without RDS and their parents; twins born prematurely or at term with or without RDS and their parents; and families with more than one individual with RDS.